1. Field of the Invention
The present invention relates to a method for detecting defects on a transparent film in a scanner, and more specifically to a method that lengthens or shortens the exposure time to detect defects on a transparent film in a scanner.
2. Description of the Prior Art
As computer technology develops, peripheral devices also change with each passing day. The scanner is an excellent example of this. Scanners are used to scan a transparent film so as to obtain corresponding digital image signals. In general, the film is easily contaminated by dust and hair, or easily scratched. As a result, defects will be formed on the film and damage the scanned image. Therefore, high quality scanners always have the function of repairing the defects.
Please refer to FIG. 1. FIG. 1 is a functional block diagram of a prior art scanner 10. The scanner 10 is used to scan a transparent film 14. The scanner 10 comprises a white light source 12a, an infrared light source 12b, and a light sensor 16. The white light source 12a is used to generate white light, and the infrared light source 12b is used to generate infrared light. The white light is composed of red light, green light and bluelight. The light sensor 16 comprises a plurality of red light charge-coupled devices 16a arranged in order, a plurality of green light charge-coupled devices 16b arranged in order, and a plurality of blue light charge-coupled devices 16c arranged in order. The charge-coupled devices 16a, 16b and 16c each generate a corresponding electric charge when the white light passes through the transparent film 14. In addition, the light sensor 16 further comprises a plurality of infrared charge-coupled devices 16d arranged in order for generating a corresponding electric charge in the charge-coupled devices 16d when the infrared light passes through the transparent film 14. A computer system 18 electrically connects with the light sensor 16 for processing the output of the light sensor 16.
Please refer to FIG. 2. FIG. 2 is a flow chart showing how the prior art scanner 10 detects defects on the transparent film 14. The procedures of the prior art method for detecting defects on the transparent film 14 are: Step 22:Switch on the white light source 12a and scanning the transparent film 14 so as to obtain white light image signals;Step 24:Switch on the infrared light source 12b and scan the transparent film 14 so as to obtain infrared image signals;Step 26:Find out the defect positions according to the white light image signals and the infrared image signals; andStep 28:Use the computer system 18 to repair the defect positions.
In step 22 and step 24, the white light source 12a and infrared light source 12b generate white light and infrared light respectively, so as to scan the transparent film 14. After that, the white light image signals and infrared image signals will be obtained. The infrared light can pass through transparent film 14, but not transparent film 14 with the defects of dirt and scratches. The response speed of the infrared charge-coupled device 16d to the infrared light is the fastest compared with the response speed of the red light charge-coupled device 16a to the red light, green light charge-coupled device 16b to the green light, and the blue light charge-coupled device 16c to the blue light. That means the plurality of infrared light charge-coupled devices 16d arranged in order will quickly reach a saturation level after receiving the infrared light. Therefore, after step 24 is finished, the digital image signals, which are generated by the unsaturated infrared charge-coupled device 16d, represent the image signals generated by the defects of the dirt or the scratches. Therefore, the computer system 18 is able to detect the defect positions of the dirt or the scratches according to the output of the infrared charge-coupled device 16d. The computer system 18 then uses a software operation to repair and process the corresponding defect positions of the scanned image signals, so as to obtain image signals without defects of dirt or scratches and achieve the purpose of removing the dirt or scratches from the image.
However, to scan transparent film 14, the prior art scanner 10 needs to have the infrared light source 12b and the plurality of infrared charge-coupled devices 16d installed when it scans the transparent film 14. This will complicate the mechanical design of the scanner and make fabrication more difficult, increasing the cost.
It is therefore a primary objective of the claimed invention to provide a method for detecting defects on a transparent film in a scanner, to overcome the shortcomings of the prior art.
The claimed invention, briefly summarized, discloses a method for detecting defects on a transparent film in a scanner. The scanner has a light source for the transparent film. The method includes using the light source to expose the transparent film for a first predetermined time to generate a first image, using the light source to expose the transparent film for a second predetermined time to generate a second image, and comparing differences between the first image and the second image according to a time ratio of the first predetermined time and the second predetermined time so as to detect the defects on the transparent film.
It is an advantage that the method of the claimed invention does not need to install the infrared light source and infrared charge-coupled device. This not only reduces the cost of the electric system, but also simplifies the mechanical design of the scanner.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.